The invention relates to a torque delivering power tool for tightening threaded joints to a desired final pretension level.
In particular, the invention concerns a power tool of the above type having a housing, a rotation motor, an output shaft connectable to a threaded joint to be tightened, power transmitting means connecting the motor to the output shaft, and a first torque transducer associated with the power transmitting means and exposed to torque magnitudes corresponding to delivered torque magnitudes up to the desired final pretension level.
A problem concerned with torque delivering power tools of the above type is the difficulty to obtain a signal from the torque transducer that reliably indicates both the torque magnitudes at the desired final pretention level and minor deviatons in the torque resistance during the low torque running down phase. It is most desirable to detect such small torque deviations since they indicate occurring thread damage, misalignment between threaded parts, or other faults that if not detected and the tightening is not stopped may cause serious damage to the screw joint and the parts being assembled.
The main object of the invention is to create a torque delivering power tool having an improved torque sensing means by which the above problem is solved.